Doctors for paper making machines



Feb. 25, 1964 H. E. B. sco'r'r noc'roas FOR PAPER MAKING mcumss 3Sheets-Sheet 1 Filed March 26, 1962 Feb. 25, 1964 H. E. B. SCOTT DOCTORSFOR PAPER MAKING MACHINES 3 Sheets-Sheet 2 Filed March 26, 1962 Feb. 25,1964 H. E. B. SCOTT 3,121,904

DOCTORS FOR PAPER MAKING MACHINES Filed March 26, 1962 s Sheets-Sheet :5

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United States Patent 3,121,904 DQCTGRS FQR PAPER MAIQNG MACHENES HaroldEric Baliol Scott, The Heath, Weyhridge, England, assignor to VickerysLimited, London, England Filed Mar. 26, 1962, Ser. No. 182,338 (Ilaimspriority, application Great Britain Apr. 7, 1961 4 Claims. (Cl.15--3t)3) With the increasing speed of papermaking machines and themodern practice of coating the paper web with china clay, titaniumdioxide and other fillers to increase the opacity while the paper isbeing made on the machine, fuzz and dust particles removed from therolls and especially from the drying cylinders by the doctors create aproblem.

The present invention provides a doctor which includes a suction chamberextending lengthwise of the doctor, a number of spaced suction nozzlesextending from the suction chamber and terminating in suction orificessituated close to the tip of the doctor blade at the side thereof remotefrom the roll to which the doctor is applied, the suction nozzlesproviding a substantially uniform distribution of airflow across thewidth of the doctor, and a deflector plate extending across the suctionnozzles and down to the doctor blade for guiding broken paper web awayfrom the doctor blade and preventing it from bunching-up around thesuction nozzles, the deflector plate having openings opposite thesuction orifices and forming one side of a closed chamber surroundingthe suction nozzles.

Two alternative forms of doctor according to the invention areillustrated, by way of example, in the accompanying drawings in which:

FIG. 1 is a cross section through the first form of doctor,

FIG. 2 is a broken away view looking in the direction of the arrow A inFIG. 1,

FIG. 3 is a section on the line IIIIH in FIG. 2,

FIG. 4 is a cross section through the second form of doctor,

FIG. 5 is a view similar to FIG. 4 showing the deflector plate sprungaway from the nozzles and FIG. 6 is a section through one of the suctionnozzles taken at right angles to the View shown in FIG. 4.

Like reference numerals designate like parts in all the figures.

Referring first to FIGS. 1-3 the doctor includes a blade 10 and apressure plate 11 which bears on the blade 10 throughout its width. Theblade 10 and pressure plate 11 are mounted in a holder 12 attached to asupport 13 which is suitably biased to maintain the tip of the blade 10in contact with the roll to be doctored.

On the support 13 is mounted a pear-shaped member which defines with thesupport a suction chamber 14, extending for the full length of thedoctor and to which suction is applied by any suitable means. A numberof suction nozzles 15 extend forwardly from the chamber 14 and terminatein suction orifices 16 near the tip of the blade 10. The nozzles 15 varyin area across the doctor so as to maintain an even distribution of airflow across the doctor. To this end the size of the suction nozzles 15increases progressively from the end of the chamber 14 to which suctionis applied to the other end of said chamber. The nozzles 15 are locatedin a closed chamber 17, the ends of which are closed by the end walls ofthe suction chamber 14 and the front wall of which is formed by adeflector plate 18 which bears at its lower end on the pressure plate 11and normally abuts against the ends of the nozzles 15 to form a sealpreventing the entry of atmospheric air into the chamber 17. The rearwall of the chamber 17 is constituted by a plate 30, secured to thesuction chamber 14 by screws 31 and having openings 34 registering withthe suction nozzles 15. The nozzles 15 have flanges 32 at their rearends which are formed with holes 33 to accommodate screws (not shown)for fixing the nozzles 15 to the plate 30. The deflector plate 18 whichextends above the tubular nozzles 15 from the suction chamber 14 to thepressure plate 11, has openings 19 in register with the orifices 16. Thedeflector plate 18 has a smooth surface and guides upwardly over the topof the chamber 14 any broken web, so preventing it from launching-uparound the nozzles 15 or other parts of the doctor. The openings 19 haveinwardly bent lips 21) at their upper edges in order to prevent theleading edge of the broken web from catching in the openings. Whenpressure is applied to the blade 10, the deflector plate 18 springsslightly away from the nozzles 15, but since the chamber 17 is closed,air continues to be drawn into the nozzles 15 through the openings 19without substantial diminution of suction to the openings 19 and thepressure in the chamber 17 is reduced to a value slightly belowatmospheric pressure.

The doctor shown in FIG. 4 is very similar to that just described, butin this case the suction chamber is constituted by a tube 14A whichmakes airtight contact with the support 13 to allow sub-atmosphericpressure to be maintained in the chamber 17' or may be attached to thesupport 13. As will be noted the nozzles 15 and deflector plate 18' ofFIG. 4 difler slightly in configuration from the corresponding parts ofFIG. 1. The nozzles 15 are shown in FIG. 6 attached by screws 35 to thetube 14A which constitutes the rear wall of the closed chamber 17 Aswill be apparent from the foregoing description, it is characteristic ofthe invention that the suction nozzles are located in a closed chamberwhich is maintained at sub-atmospheric pressure.

What I claim as my invention and desire to secure by Letters Patent is:

l. A doctor for a roll of a paper making machine comprising a support, adoctor blade carried by said support, a pressure plate also carried bythe support and bearing on the doctor blade throughout its length, wallmeans cooperating with the support to form a suction chamber thereon andextending lengthwise of the doctor blade, a number of spaced tubularsuction nozzles extending from said suction chamber towards the doctorblade and terminating in suction orifices situated near the tip of thedoctor blade, said suction nozzles providing a substantially uniformdistribution of airflow across the length of the doctor, and a closedchamber surrounding said nozzles and having two of its walls defined bythe support and by a deflector plate which extends over the suctionnozzles from the suction chamber to the pressure plate, said deflectorplate guiding broken web away from the doctor blade and over the suctionchamber and having openings opposite the suction orifices.

2. A doctor as claimed in claim 1, in which the edges of the openings inthe deflector plate remote from the doctor blade are bent inwardly.

3. A doctor as claimed in claim 1, in which the suction chamber isdefined by the support and by a pear shaped casing attached to thesupport.

4. A doctor as claimed in claim 1, in which the wall means is a tubemounted on the support of the doctor to make airtight contact therewith.

References Cited in the file of this patent UNITED STATES PATENTS2,890,473 Scott June 16, 1959 FOREIGN PATENTS 821,490 Great Britain Oct.17, 1959

1. A DOCTOR FOR A ROLL OF A PAPER MAKING MACHINE COMPRISING A SUPPORT, ADOCTOR BLADE CARRIED BY SAID SUPPORT, A PRESSURE PLATE ALSO CARRIED BYTHE SUPPORT AND BEARING ON THE DOCTOR BLADE THROUGHOUT ITS LENGTH, WALLMEANS COOPERATING WITH THE SUPPORT TO FORM A SUCTION CHAMBER THEREON ANDEXTENDING LENGTHWISE OF THE DOCTOR BLADE, A NUMBER OF SPACED TUBULARSUCTION NOZZLES EXTENDING FROM SAID SUCTION CHAMBER TOWARDS THE DOCTORBLADE AND TERMINATING IN SUCTION ORIFICES SITUATED NEAR THE TIP OF THEDOCTOR BLADE, SAID SUCTION NOZZLES PROVIDING A SUBSTANTIALLY UNIFORMDISTRIBUTION OF AIRFLOW ACROSS THE LENGTH OF THE DOCTOR, AND A CLOSEDCHAMBER SURROUNDING SAID NOZZLES AND HAVING TWO OF ITS WALL DEFINED BYTHE SUPPORT AND BY A DEFLECTOR PLATE WHICH EXTENDS OVER THE SUCTIONNOZZLES FROM THE SUCTION CHAMBER TO THE PRESSURE PLATE, SAID DEFLECTORPLATE GUIDING BROKEN WEB AWAY FROM THE DOCTOR BLADE AND OVER THE SUCTIONCHAMBER AND HAVING OPENINGS OPPOSITE THE SUCTION ORIFICES.